1. Field of the Invention
This invention relates to method and apparatus for folding a cardboard sheet along a straight fold line, and to a cardboard sheet folded by the method. Cardboard is also known as paperboard, but the former term will be used in this specification and claims.
2. Description of the Prior Art
In one known method of folding a cardboard sheet, a first surface of the sheet is located against a first element having a straight edge at the location where fold line is to be formed, the second surface of the cardboard sheet is located against a support surface and a second element pushed the second surface of the cardboard sheet so as to fold the sheet around the said edge, thereby forming the fold line in the sheet at said edge. Illustrative disclosures of this known process as in U.S. Pat. Nos. 2,283,159, 2,477,355, German Pat. No. 555,202 and Dutch published Pat. application No. 7,705,944.
This known process suffers from a major defect. When the cardboard sheet is folded around an edge, the fibres of the board on the outside of the fold are stretched and rupture, so that the cardboard loses strength considerably along the fold line.